U.S. patent application number 11/667595 was filed with the patent office on 2009-05-21 for method for multicode transmission by a subscriber station.
Invention is credited to Volker Breuer, Thomas Ulrich.
Application Number | 20090131027 11/667595 |
Document ID | / |
Family ID | 35478457 |
Filed Date | 2009-05-21 |
United States Patent
Application |
20090131027 |
Kind Code |
A1 |
Breuer; Volker ; et
al. |
May 21, 2009 |
METHOD FOR MULTICODE TRANSMISSION BY A SUBSCRIBER STATION
Abstract
In a radio communications system, several codes for transmitting
messages are assigned to a subscriber station. A transmission power
differential is determined between the total maximum transmission
power of the subscriber station for the codes and the total
transmission power of the subscriber station for the codes at the
beginning of a message transmission, (the differential being
respected by the subscriber station), by a first one of the
codes.
Inventors: |
Breuer; Volker; (Botzow,
DE) ; Ulrich; Thomas; (Bad Durkheim, DE) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700, 1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Family ID: |
35478457 |
Appl. No.: |
11/667595 |
Filed: |
October 6, 2005 |
PCT Filed: |
October 6, 2005 |
PCT NO: |
PCT/EP2005/055037 |
371 Date: |
December 22, 2008 |
Current U.S.
Class: |
455/418 |
Current CPC
Class: |
H04W 52/50 20130101;
H04W 52/34 20130101 |
Class at
Publication: |
455/418 |
International
Class: |
H04M 3/00 20060101
H04M003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2004 |
DE |
10 2004 054 626.6 |
Claims
1-11. (canceled)
12. A method for operating a radio communication system in which a
subscriber station is assigned a plurality of codes for
transmitting messages, comprising: determining a transmit power
difference which is to be maintained by the subscriber station
between on one hand a total maximum transmit power of the
subscriber station for the codes and on another hand a total
transmit power of the subscriber station for the codes at a start
of a message transmission using a first one of the codes.
13. The method as claimed in claim 12, wherein said determining of
the transmit power difference is performed by a network device, and
wherein said method further comprises sending from a base station
to the subscriber station a message containing information relating
to the transmit power difference as determined by the network
device.
14. The method as claimed in claim 13, wherein the message to the
subscriber station contains information relating to a maximum data
rate to be used by the subscriber station for the message
transmission using the first code.
15. The method as claimed in claim 14, wherein said determining of
the transmit power difference is based on a function of at least
one of a property of the base station, a property of a radio cell
of the base station, an interference situation, at least one
service used by the subscriber station, and a classification of the
subscriber station.
16. The method as claimed in claim 13, wherein said determining of
the transmit power difference is based on a function of at least
one of a property of the base station, a property of a radio cell
of the base station, an interference situation, at least one
service used by the subscriber station, and a classification of the
subscriber station.
17. The method as claimed in claim 12, wherein said determining of
the transmit power difference is performed by the subscriber
station.
18. The method as claimed in claim 17, wherein said determining of
the transmit power difference is based on a function of a plurality
of transmit powers used previously by the subscriber station for a
second of the codes.
19. The method as claimed in claim 18, wherein the radio
communication system is a Universal Mobile Telecommunications
System radio communication system.
20. A method for operating a radio communication system in which a
subscriber station is assigned a plurality of codes for
transmitting messages, comprising: maintaining a previously
determined transmit power difference by the subscriber station
between on one hand a total maximum transmit power of the
subscriber station for the codes and on another hand a total
transmit power of the subscriber station for the codes at a start
of a message transmission using a first one of the codes.
21. The method as claimed in claim 20, wherein the transmit power
difference is determined on the network side and a base station
sends the subscriber station a message containing information
relating to the defined transmit power difference.
22. The method as claimed in claim 21, wherein the message to the
subscriber station contains information relating to a maximum data
rate to be used by the subscriber station for the message
transmission using the first code.
23. The method as claimed in claim 22, wherein said determining of
the transmit power difference is based on a function of at least
one of a property of the base station, a property of a radio cell
of the base station, an interference situation, at least one
service used by the subscriber station, and a classification of the
subscriber station.
24. The method as claimed in claim 21, wherein said determining of
the transmit power difference is based on a function of at least
one of a property of the base station, a property of a radio cell
of the base station, an interference situation, at least one
service used by the subscriber station, and a classification of the
subscriber station.
25. The method as claimed in claim 20, wherein said determining of
the transmit power difference is performed by the subscriber
station.
26. The method as claimed in claim 25, wherein said determining of
the transmit power difference is based on a function of a plurality
of transmit powers used previously by the subscriber station for a
second of the plurality of codes.
27. The method as claimed in claim 26, wherein the radio
communication system is a Universal Mobile Telecommunications
System radio communication system.
28. A base station in a radio communication system in which a
subscriber station is assigned a plurality of codes for
transmitting messages, comprising: means for determining a transmit
power difference which is to be maintained by the subscriber
station between on one hand a total maximum transmit power of the
subscriber station for the codes and on another hand a total
transmit power of the subscriber station for the codes at a start
of a message transmission using a first one of the codes.
29. A subscriber station for a radio communication system, the
subscriber station assigned a plurality of codes for transmitting
messages, comprising: means for determining a transmit power
difference which is to be maintained by the subscriber station
between on one hand a total maximum transmit power of the
subscriber station for the codes and on another hand a total
transmit power of the subscriber station for the codes at a start
of a message transmission using a first one of the codes.
30. A subscriber station as claimed in claim 29, further comprising
means for maintaining the transmit power difference.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based on and hereby claims priority to
German Application No. 10 2004 054 626.6 filed on Nov. 11, 2004,
the contents of which are hereby incorporated by reference.
BACKGROUND
[0002] Described below are methods for operating a radio
communication system wherein a subscriber station is assigned a
first and a second code for the purpose of transmitting
messages.
[0003] In radio communication systems, messages containing, for
example, voice information, image information, video information,
SMS (Short Message Service), MMS (Multimedia Messaging Service) or
other data are transmitted between a transmitting radio station and
a receiving radio station via a radio interface with the aid of
electromagnetic waves. Depending on the physical embodiment of the
radio communication system, the radio stations in this case can be
different types of subscriber radio stations or network-side radio
stations such as base stations. In a mobile radio communication
system at least some of the subscriber stations are mobile radio
stations. The electromagnetic waves are emitted by carrier
frequencies that lie in the frequency band provided for the
respective system.
[0004] Mobile radio communication systems are often embodied as
cellular systems, for example conforming to the GSM (Global System
for Mobile Communication) or UMTS (Universal Mobile
Telecommunications System) standard, having a network
infrastructure formed of base stations, devices for monitoring and
controlling the base stations and further network-side equipment.
Apart from these cellular, hierarchical radio networks organized as
wide area (supralocal) networks there are also wireless local
networks such as, for example, WLANs (Wireless Local Area Networks)
having a radio coverage area that is generally considerably more
limited geographically. The cells covered by the radio access
points (AP: Access Point) of the WLANs are usually small compared
with typical mobile radio cells. Examples of different standards
for WLANs are HiperLAN, DECT, IEEE 802.11, Bluetooth and WATM.
[0005] Access by subscriber stations to the common transmission
medium is controlled in radio communication systems by multiple
access (MA) methods/multiplex methods. With these multiple access
techniques the transmission medium can be divided up between the
subscriber stations in the time domain (Time Division Multiple
Access, TDMA), in the frequency domain (Frequency Division Multiple
Access, FDMA), in the code domain (Code Division Multiple Access,
CDMA) or in the space domain (Space Division Multiple Access,
SDMA). Combinations of multiple access methods are also
possible.
[0006] With code division multiple access methods,
subscriber-specific codes are used for communication with
subscriber stations, with the result that in the downlink direction
the respective subscriber station or, as the case may be, in the
uplink direction network-side devices can differentiate the
messages to or from the subscriber station from the messages to or
from other subscriber stations by establishing a correlation
between the received signal and the subscriber-specific code. It is
possible for a subscriber station to use a plurality of codes for
transmitting messages. In this case the different codes serve to
distinguish different transmission channels used by the subscriber
station, such as, for example, to distinguish between channels for
transmitting payload and signaling information, or to distinguish
channels of different services.
SUMMARY
[0007] An aspect is to disclose an efficient method for operating a
radio communication system wherein a subscriber station is assigned
a first and a second code for the purpose of transmitting messages.
Devices for performing the method are also to be presented.
[0008] According to a first method for operating a radio
communication system, a subscriber station is assigned a plurality
of codes for transmitting messages. A transmit power difference to
be maintained by the subscriber station is determined between on
the one hand the total maximum transmit power of the subscriber
station for the plurality of codes and on the other hand the total
transmit power of the subscriber station for the plurality of codes
at the start of a message transmission using a first of the
plurality of codes.
[0009] According to a second method for operating a radio
communication system wherein a subscriber station is assigned a
plurality of codes for transmitting messages, a previously
determined transmit power difference is maintained by the
subscriber station between on the one hand the total maximum
transmit power of the subscriber station for the plurality of codes
and on the other hand the total transmit power of the subscriber
station for the plurality of codes at the start of a message
transmission using a first of the plurality of codes.
[0010] The subscriber station is assigned at least a first and a
second code for the purpose of transmitting messages. Each of the
different codes can be a combination of a plurality of individual
codes; thus, according to UMTS, for example, the combination
consisting of a spreading and a scrambling code. In addition to the
plurality of codes that are involved in the method described below,
further codes can also be used by the subscriber station for the
purpose of transmitting messages.
[0011] A transmit power difference which is to be maintained by the
subscriber station between a first and a second transmit power is
determined. A difference between two values is maintained if the
distance between the two values is greater than or equal to the
difference. The first of the two transmit powers is the total
maximum transmit power of the subscriber station for the plurality
of codes, i.e. the maximum transmit power, when the subscriber
station uses the plurality of codes in parallel for transmitting
messages. The maximum transmit power for the parallel use of a
plurality of codes is preferably predetermined by the hardware of
the subscriber station, which is to say, for example, by the power
amplifier which is intended to amplify in a linear manner but
produces a non-linear signal distortion in the power end range, for
which reason it is not used in the end range. It is, however, also
possible for the maximum transmit power for the parallel use of a
plurality of codes of the subscriber station to be predefined on
the network side.
[0012] The second of the two transmit powers is the total transmit
power of the subscriber station for the plurality of codes at the
start of a message transmission using a first of the codes. This
corresponds to the sum of the transmit power for the first code and
the transmit power for the remaining code or codes, and moreover in
each case at the time of the start of the message transmission
using the first code. If no message transmission using the
remaining code or codes is performed precisely at the time of the
start of the message transmission using the first code, but instead
is only initiated a short time later, then the transmit power for
the remaining code or codes at the point in time occurring a short
time later can be used for the sum forming operation described.
[0013] If messages are transmitted using the first code at specific
time intervals rather than continuously, the start of a time
interval of this kind corresponds to the start of the message
transmission using the first code. The method described below can
be applied in relation to any such start time, i.e. to any message
transmission using the first code, or to a subset of the start
times.
[0014] The radio communication system under consideration can be a
cellular mobile radio communication system, in particular a UTMS
radio communication system, or also a local radio communication
system.
[0015] the transmit power difference may be determined on the
network side and a base station sends the subscriber station a
message containing information relating to the determined transmit
power difference. In this case the transmit power difference is
determined not by the subscriber station, but by one or more
devices of the infrastructure network of the radio communication
system, in particular by the base station. After the network-side
determination of the transmit power difference, information
relating to the determined transmit power difference is notified to
the subscriber station so that the subscriber station can extract
the transmit power difference from the information or determine the
transmit power difference from the information.
[0016] It is advantageous if the message to the subscriber station
also contains information relating to a maximum data rate to be
used by the subscriber station for the message transmission using
the first code.
[0017] The transmit power difference may be determined as a
function of a property of the base station and/or the radio cell of
the base station, and/or of an interference situation, and/or of at
least one service used by the subscriber station, and/or of a
classification of the subscriber station. In this way the transmit
power difference can be defined differently from base station to
base station or, as the case may be, from radio cell to radio cell
under conditions that are otherwise identical. With regard to the
interference, the interference within the cell to which the
subscriber station is assigned, and/or within cells adjacent to
this cell, can be taken into account. It is advantageous in
particular to take into account the type of service used by the
subscriber station by transmitting messages using the first code
during the determination of the transmit power difference.
Subscriber stations can be classified or prioritized on the network
side and handled in accordance with this classification during the
determination of the transmit power difference.
[0018] The transmit power difference may be determined by the
subscriber station. This difference can be determined in particular
as a function of a plurality of transmit powers used in the past by
the subscriber station for a second code, in particular using the
variance of these transmit powers. This taking into account of the
transmit powers used in the past can also be indirect, in that
power control information received by the subscriber station in
respect of the transmit powers used for the second code is
used.
[0019] The network-side device and the subscriber station can have
a transmit power difference which is to be maintained by the
subscriber station between, on the one hand, the total maximum
transmit power of the subscriber station for the plurality of codes
and, on the other hand, the total transmit power of the subscriber
station for the plurality of codes at the start of a message
transmission using a first of the plurality of codes.
[0020] In addition or alternatively, the subscriber station can
maintain a previously determined transmit power difference between,
on the one hand, the total maximum transmit power of the subscriber
station for the plurality of codes and, on the other hand, the
total transmit power of the subscriber station for the plurality of
codes at the start of a message transmission using a first of the
plurality of codes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] These and other objects and advantages will become more
apparent and more readily appreciated from the following
description of an exemplary embodiment, taken in conjunction with
the accompanying drawings of which:
[0022] FIG. 1 is a pictorial diagram of a portion of a radio
communication system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] Reference will now be made in detail to the preferred
embodiments, examples of which are illustrated in the accompanying
drawings, wherein like reference numerals refer to like elements
throughout.
[0024] FIG. 1 shows a section of a UMTS radio communication system
with a subscriber station UE (UE: User Equipment) and a base
station NODE B. The base station NODE B is connected to further
network-side devices of the infrastructure network NET. In the
uplink (UL) direction the communication, i.e. the message
transmission from the subscriber station UE to the base station
NODE B, takes place on a dedicated channel, described, for example,
in [3GPP TS 25.211 V6.2.0, 3rd Generation Partnership Project;
Technical Specification Group Radio Access Network; Physical
channels and mapping of transport channels onto physical channels
(FDD)]. For this purpose the subscriber station UE is assigned the
code DCH. A second code EDCH (Enhanced Dedicated Uplink Channel) is
assigned to the subscriber station UE, in particular for
transmitting high bit rate traffic.
[0025] In order to regulate the power in accordance with a closed
loop power control, the base station NODE B sends the subscriber
station UE power control instructions, the TPC bits, at regular
intervals, i.e. information as to whether the transmit power is to
be increased or decreased by the subscriber station UE. The
subscriber station UE is subject to a maximum value for the
transmit power which cannot be exceeded. In deteriorating radio
transmission conditions the subscriber station UE is requested by
the base station NODE B to increase its transmit power. The
transmit power can be increased at most up to the maximum value of
the transmit power of the subscriber station UE. If the subscriber
station UE receives a further request to increase its transmit
power after reaching the maximum value of its transmit power, it
can adjust the TFC (Transport Format Combination) used by it. For
each physical channel the TFC specifies the ratio of coded data,
i.e. the total data, to the payload data, and consequently the data
rate. For a given radio channel each TFC is uniquely linked to a
transmit power. Under constant radio traffic conditions, therefore,
a switch to a TFC with a lower data rate corresponds to a switch to
a lower transmit power. In order to comply with the request of the
base station NODE B for a transmit power increase, the subscriber
station UE can thus switch to a TFC with a lower data rate and
leave the transmit power unchanged or reduce it. The switching of a
TFC can only take place at specific times, and moreover at specific
TTI limits (TTI: Transmission Time Interval).
[0026] If the subscriber station UE uses not just the code DCH, but
the two codes EDCH and DCH in parallel, the situation in which the
subscriber station UE reaches the maximum value of its transmit
power occurs more often than if the subscriber station UE uses only
the code DCH. There are the following reasons for this: [0027] The
total transmit power of the subscriber station UE when using a
plurality of codes is produced from the sum of the transmit powers
of the individual codes. The total transmit power of the subscriber
station UE is therefore higher on average, the more codes it uses.
[0028] The code EDCH is intended to be used for transmitting high
bit rate data packets to the base station NODE B. In keeping with
the link between data rate and transmit power via the TFC, the
subscriber station UE requires a higher transmit power for the code
EDCH than for the code DCH. [0029] If the subscriber station UE
uses the two codes EDCH and DCH in parallel, the maximum value of
the transmit power can be reduced compared with the case where it
uses only the code DCH. The reason for this is that in a multicode
transmission the PAR value (PAR: Peak to Average Ratio) can be
worse. This reduction in the maximum transmit power in a multicode
transmission applies to most subscriber stations; if this reduction
were to be avoided, higher requirements in terms of the linearity
of the amplifiers of the subscriber stations would be
necessary.
[0030] The length of an EDCH message (TTI: Transmission Time
Interval) is 10 ms. During this time the subscriber station UE
receives 15 TPC bits. The TFC for the code EDCH cannot be changed
during the TTI, i.e. the subscriber station UE can respond to an
instruction from the base station NODE B to increase its transmit
power only by increasing the transmit power; adjusting the TFC for
the code EDCH is not possible during the transmission of an EDCH
message. Another possible way to respond to the request from the
base station NODE B to increase the transmit power is to adjust the
TFC for the code DCH. This can be switched by the subscriber
station UE at the start of a TTI for the code DCH. The times of the
TTI start of the two codes DCH and EDCH can be different from each
other. In this way it is possible for the subscriber station UE to
comply with the request to increase the transmit power during the
transmission of an EDCH message by changing the TFC for the code
DCH and thereby enabling the transmit power for the code EDCH to be
increased if a suitable TTI limit for switching over the TFC is
present. This is only possible, however, if the subscriber station
UE is not already using the lowest possible data rate for the code
DCH. However, this smallest TFC corresponding to the lowest
possible data rate is always used by the subscriber station UE when
it has little data to be transmitted using the code DCH.
[0031] If when using the two codes EDCH and DCH the subscriber
station UE reaches the (reduced) maximum value of the transmit
power during the transmission of an EDCH message, and if it
receives instructions from the base station NODE B to continuously
increase its transmit power, it must abort the transmission of the
EDCH message before the end of the EDCH message if an adjustment of
the TFC of the code DCH is not possible. Aborting the message
transmission of the code DCH is not possible, for if the base
station NODE B can no longer receive the messages of the code DCH,
the connection between the base station NODE B and the subscriber
station UE is interrupted, with the result that the maintaining of
the communication using the code DCH for upholding the connection
between subscriber station UE and base station NODE B is
indispensable. Aborting the transmission of the EDCH message means
wasting radio resources, since the incomplete EDCH message cannot
be evaluated on the network side, yet interference has been
generated due to the incomplete transmission of the EDCH
message.
[0032] The subscriber station UE is notified by the base station
NODE B prior to the transmission of an EDCH message of which TFC
may be used at a maximum for this transmission, i.e. the maximum
possible data rate for the EDCH message. Before the transmission of
the EDCH message the subscriber station UE specifies a TFC which
will be used for the EDCH message, taking into account that the
maximum data rate assigned to it by the base station NODE B may not
be exceeded. According to the radio traffic conditions or, as the
case may be, the radio channel between the subscriber station UE
and the base station NODE B, a specific transmit power for the
transmission of the EDCH message is linked to the selected TFC
under constant propagation conditions.
[0033] If the subscriber station UE chooses a high data rate and
therefore a high transmit power for the transmission of the EDCH
message, it is possible that it will receive a request to increase
the transmit power several times during the transmission of the
EDCH message, which ultimately can lead, as described in the
foregoing, to the abortion of the transmission of the EDCH message
since the maximum transmit power of the subscriber station UE would
have been exceeded. If, on the other hand, the subscriber station
UE chooses a low data rate and therefore a low transmit power for
the transmission of the EDCH message, it is possible that if there
are few requests to increase the transmit power a large part of the
total transmit power available to the subscriber station UE will
not be used and consequently a lower data rate was used for the
EDCH message than would be possible and desirable from the point of
view of the subscriber station UE. In selecting the TFC for the
transmission of an EDCH message a compromise must therefore be
found between a high data rate for the EDCH message and a reliable,
i.e. complete, transmission of the EDCH message.
[0034] In order to solve this problem, it is proposed that a
transmit power difference which is to be maintained by the
subscriber station UE be determined by the base station NODE B. The
transmit power difference, which can be termed the "power
headroom", is required to exist between the total transmit power
for the two codes DCH and EDCH at the start of the transmission of
an EDCH message and the maximum transmit power for the two codes
DCH and EDCH. The transmit power difference thus corresponds to an
unused transmit power at the start of the transmission of an EDCH
message. For illustration purposes a numeric example will be
considered: [0035] The maximum transmit power of the subscriber
station UE when using only the code DCH, i.e. without multicode
transmission, is 21 dBm. [0036] Let the maximum transmit power of
the subscriber station UE when using the two codes DCH and EDCH be
reduced by 3 dB compared to the maximum transmit power when using
only one code, i.e. it amounts to 21 dBm-3 dB=18 dBm. [0037] For
the code DCH let the subscriber station UE use the minimum possible
data rate, this corresponding to a transmit power for the code DCH
of 3 dBm given a specific assumed radio propagation condition.
Thus, a maximum of 18 dBm-3 dB=15 dBm is available for the code
EDCH. [0038] Let the base station NODE B specify a transmit power
difference of 8 dB for the subscriber station UE. This yields the
maximum transmit power to be used by the subscriber station UE at
the start of the transmission of the EDCH message as: 18 dBm-3 dB-8
dB=7 dBm.
[0039] The transmit power difference can be determined in the base
station NODE B as a function of a number of parameters:
[0040] The Type of Cell of the Base Station NODE B.
[0041] A distinction can be made between "capacity limited" and
"coverage limited" cells. A "capacity limited" cell is a cell in
which the transmit power of the base station that is to be divided
up among the subscriber stations in the downlink direction is the
limiting factor for the cell size. This applies mostly to small
cells in urban areas. The subscriber stations in such cells
generally transmit at low transmit power, so the maximum transmit
power of the subscriber stations is seldom reached. No large "power
headroom" must therefore be set for a "capacity limited" cell, i.e.
a base station of a "capacity limited" cell defines only small
transmit power differences. A "coverage limited" cell is a cell in
which the transmit power of the subscriber stations in the uplink
direction is the limiting factor for the cell size. This applies
mostly to large cells in rural areas. Since the subscriber stations
of a "coverage limited" cell frequently reach their maximum
transmit power, a large "power headroom" should be set at the start
of the transmission of an EDCH message to ensure that sufficient
scope for increasing the transmit power during the transmission of
the EDCH message is present. A base station of a "coverage limited"
cell will therefore define high transmit power differences.
[0042] The Current Interference Situation in the Cell or in an Area
Formed by a Plurality of Cells.
[0043] The greater the current interference in a cell and/or in the
surrounding cells, the higher the transmit power differences should
be specified. The consequence of this is that subscriber stations
which are located in the vicinity of the receiving base station and
which therefore require a low transmit power and so generate little
interference receive preference, i.e. achieve greater data rates
for the EDCH messages than the more remote subscriber stations.
Owing to the fact that the subscriber stations in the vicinity of
the base station must use only low transmit powers to achieve high
data rates, their EDCH transmissions scarcely experience any
restrictions due to large transmit power differences. In contrast,
subscriber stations which are very distant from the base station
are subject to restrictions in respect of the transmission of EDCH
messages, since only a low data rate is possible for the EDCH
messages due to the great distance from the receiving base station
or during the soft handover to the receiving base stations and due
to the high transmit power difference, with the consequence that
many of these subscriber stations must forego the transmission of
EDCH messages. As a result the subscriber stations generate little
interference in the surrounding cells. Specifying the transmit
power difference thus represents a controlling intercell
interference.
[0044] The Service Used by a Subscriber Station in Respect of the
Code EDCH.
[0045] A distinction can be made between two basic types of
services. Firstly there are services in which a minimum service
rate is guaranteed (referred to as the Guaranteed Bit Rate, or
GBR). These can be realtime services in which a reliable
transmission is necessary, such as, for example, videotelephony and
online gaming. A high transmit power difference should be specified
for these services so that even if the radio channel deteriorates
during the transmission of an EDCH message this can be made up for
by an increase in the transmit power and the EDCH message can be
transmitted without having to be aborted. Secondly there are
services in which a high data rate is required, while an occasional
breakdown in the transmission of an EDCH message does not have an
overly negative impact. The aborted EDCH messages can be
transmitted in full at a later time. Examples of this are
non-realtime games. A low transmit power difference should be
specified for the latter-mentioned services to ensure that a high
data rate (maximum throughput) can be achieved for the EDCH
messages.
[0046] The Strategy of the Network Operator in Respect of the
EDCH.
[0047] If a high data throughput is to be achieved overall for all
users via the EDCH, low transmit power differences should be
defined by the base stations.
[0048] The Class of the Subscriber Station.
[0049] The subscriber stations can be classified, with subscriber
stations belonging to a higher priority class having to maintain a
lower transmit power difference than subscriber stations belonging
to a lower priority class. Threshold values, for example, can be
used as maximum values of the transmit power difference for
subscriber stations belonging to certain classes. The lowering of
the transmit power difference as the priority of the subscriber
stations increases can be explained by the fact that the base
station must divide up the total interference that is tolerable for
the EDCH at its receiver for the EDCH channel of all subscriber
stations between the subscriber stations. In particular the
subscriber stations which are at a great distance from the base
station generate an increased amount of interference. Using a low
transmit power difference, a high priority subscriber station is
allocated a large proportion of the interference that is to be
divided up between the subscriber stations. When a high transmit
power difference is to be maintained a subscriber station can
decide that the respective data rate for the EDCH message is so
small that it will dispense with the transmission of the EDCH
message. If a high value for the transmit power difference is
determined for the subscriber stations when a high level of
interference is present, it is possible at these times for EDCH
messages to be transmitted only by subscriber stations which have
been assigned a high priority, since the defined transmit power
difference is too high for the transmission of an EDCH message for
the lower priority subscriber stations. The classification can have
an effect on the billing of the respective subscriber.
[0050] When determining the transmit power difference the base
station NODE B can use one of the described parameters or
combinations of the parameters. The transmit power difference can
be determined on a subscriber-station-specific basis, i.e. for
individual subscriber stations, or for a group of subscriber
stations or for all subscriber stations which use a code EDCH.
[0051] The transmit power difference is signaled to the subscriber
station UE by the base station NODE B. It is possible that the
subscriber station UE has to maintain the transmit power difference
exactly, i.e. that the sum formed from the transmit powers for the
two codes DCH and EDCH at the start of the transmission of the EDCH
message differs from the maximum transmit power available for the
two codes DCH and EDCH precisely by the transmit power difference,
or that the transmit power difference defined by the base station
NODE B represents a minimum value which must be present at least
between the sum of the transmit powers for the two codes DCH and
EDCH at the start of the transmission of the EDCH message and the
maximum transmit power available for the two codes DCH and EDCH.
The determined transmit power difference can be signaled using a
message introduced specifically for these purposes, though the
information relating to the transmit power difference can also be
integrated into another message. It is advantageous in particular
if a message is sent from the base station NODE B to the subscriber
station UE containing both the specification of the transmit power
difference requiring to be maintained and the specification of the
TFC with the maximum data rate that may be used by the subscriber
station UE for the respective transmission of the EDCH message. If
the same transmit power difference is determined for a plurality of
subscriber stations, these can be informed of the defined transmit
power difference in a joint notification.
[0052] While the case has been described in which the transmit
power difference is determined by the base station, the transmit
power difference can also be determined by a device controlling the
base station NODE B, such as, for example, by a CRNC (Controlling
RNC). This device then informs the base station NODE B of the
defined transmit power difference. As described above in relation
to the message transmission between base station and subscriber
station, the information relating to the defined transmit power
difference is preferably contained in a message which also includes
the specification of the TFC with the maximum data rate that may be
used by the subscriber station for the respective transmission of
the EDCH message.
[0053] As an alternative to the transmit power difference being
defined by the base station NODE B, it can also be determined by
the subscriber station UE. In this case the subscriber station UE
can take into account the instructions received in the past
concerning the transmit power control in relation to the code DCH,
i.e. the TPC bits. If the transmit power for the code DCH within a
specific period of time in the past lies, for example in the range
between -10 dBm and +10 dBm, i.e. if the transmit power for the
code DCH exhibits a great variance, the transmit power difference
will be defined as a higher value by the subscriber station UE than
in the case of a small variance, which is to say, for example, if
the transmit power for the code DCH within the specific period of
time in the past lies in the range between -3 dBm and +3 dBm. Thus,
the variance of the transmit powers of a first channel, of the code
DCH, is used to determine the transmit power for a second channel,
for the code EDCH. The actual value for the transmit power of the
code EDCH is determined by the subscriber station from the transmit
power difference, the current value of the transmit power for the
code DCH, the TFC for the code EDCH, the maximum value of which is
predefined for it by the base station NODE B, its maximum transmit
power for multicode transmission, and the current radio
transmission conditions.
[0054] A description has been provided with particular reference to
preferred embodiments thereof and examples, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the claims which may include the phrase "at
least one of A, B and C" as an alternative expression that means
one or more of A, B and C may be used, contrary to the holding in
Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir.
2004).
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